Presently, most automotive carpets are manufactured using a polyester primary carpet backing. Polyester primary carpet backings have sufficiently high elongation and more plastic than elastic behavior. This type of behavior sustains stretching during carpet molding without tearing and allows the backing to remain dimensionally stable after demolding. The high glass transition temperature for polyester (about 80 degrees C. for polyethylene terephthalate (PET)) means that polyester fibers made therefrom will be dimensionally stable following the molding operation. As a result, after a molded carpet is made from a polyester primary carpet backing, the carpet will retain its shape with little tendency to shrink. In the past, polyester primary carpet backings have been the product of choice in the automotive industry due to their moldability and dimensional stability.
Polyolefin fibers, especially polypropylene fibers, are used in making primary backings for broadloom carpets. Polyolefins are less expensive than polyesters. In addition, polyolefins are easier to recycle than polyesters, due to their lower melting point, permitting melting, filtration and re-extrusion at temperatures which generally do not lead to polymer degradation. With increased emphasis on using recyclable materials, and the need to use the lowest priced materials available, it would be very desirable to be able to utilize polyolefin carpets in the automotive industry.
The polypropylene carpet backings used in broadloom carpets do not have sufficient elongation to be molded into shapes suitable for automotive carpets. Typically, the backing will tear during the molding operation. If the draw ratio of the polypropylene fibers is increased in order to increase the strength, the elongation goes down. The higher drawing process also gives higher crystallinity, exacerbating instability problems (tendency of the backing to grow or shrink) due to the lower glass transition point of polypropylene (0 degrees C.). Even if one were able to mold a polypropylene carpet backing without tearing, the molded product will tend to curl and/or lose its shape immediately or shortly after demolding due to the elastic nature of the polypropylene fibers. As a result, in the past it has been considered impossible to a make a satisfactory molded carpet using a polypropylene carpet backing.
From environmental and cost standpoints, however, a molded carpet of 100% polyolefin, especially polypropylene, is extremely desirable. Thus, there has been a long felt need to manufacture moldable, automotive carpets that are fabricated from polyolefin primary carpet backings.
U.S. Pat. No. 3,563,838 (Edwards) discloses a process for making continuous filament nonwoven fabrics. The fabrics are particularly useful as primary backings for tufted carpets since they have exceptionally high resistance to width loss on stretching and high tear strength. However, the primary carpet backings disclosed by Edwards are for use in broadloom carpets and are not directed towards making moldable carpets, such as those necessary for automotive applications.
Clearly, what is needed is a process for making a nonwoven polyolefin sheet which is useful as a primary carpet backing in moldable carpets. The process and resulting nonwoven sheet should not have, or should minimize, the deficiencies inherent in the prior art. Other objects and advantages of the present invention will become apparent to those skilled in the art upon reference to the attached drawings and to the detailed description of the invention which hereinafter follows.